Alzheimer's disease (AD) will become a public health crisis within the next 2-3 decades if left unchecked. There are no proven treatments that delay the onset or prevent the progression of AD, although several promising candidates are being developed. During the development of these therapies, it will be very important to have biomarkers that can identify individuals at high risk for AD in eariiest clinical stages in order to target them for clinical trials of disease-modifying therapies and to monitor therapy success. Clinicopathologic evidence suggests that AD pathology (particularly the buildup of amyloid plaques) begins 10-20 years before the onset of cognitive symptoms. The earliest clinical symptoms of AD are accompanied by, and likely due to, neuronal and synaptic dysfunction and/or cell death. Thus, it will be critical to identify individuals with preclinical and very early stage symptomatic AD, prior to marked clinical symptoms and neuron loss, so new therapies will have the greatest chance to preserve normal brain function. The Adult Children Study (ACS) Biomarker Core was initially funded as a competitive supplement to the ACS PPG in April 2008. The Core's mission is to facilitate and support antecedent AD biomarkers research by providing the necessary infrastructure for the collection, storage, and dissemination of fluid (CSF and plasma) samples (and associated data) for our own research at Washington University and that of the greater AD scientific community. Since inception of the Core, our productivity has roughly doubled (as defined by the number of CSF and plasma samples collected, the number of samples disseminated to investigators, and the number of papers using our samples that have been published in peer-reviewed journals). Thus, in the present renewal application, we propose to build upon our success and propose the following aims: Aim 1: Maintain and grow a repository of fasted CSF and plasma samples for present and future aging and AD biomarker studies. Aim 2: Coordinate the distribution of CSF and plasma samples to qualified investigators. Aim 3: Compare the values obtained for CSF Ap42, tau and ptauiei in Project 2 as a function of assay (Innotest vs. xMAP) and plasma Ap species (APi^o, APx-40, APi.42. APx^2) as a function of fasting state.